Method of molding concrete blocks



Feb. 13, 1951 c. w. AKERS METHOD OF MOLDING CONCRETE BLOCKS Filed Nov. 14, 1945 GHJLXRLELS PWSEQRS 3% 6W (PM l ts Wan s Patented Feb. 13, 1951 UNITEDI'STATES PATENTT' OFFICE Charles W. Akers, Nashville, Tenn.

Application November 14, 1945, Serial No. 628,502 v 1 Claim. 1

" This invention relates to improvements in the molding of heavy plastic materials such as are used in building tiles'or blocks and other build.- ing units or analogous articles.

Heretofore, in the molding of tiles, blocks and the like from heavy materials such as concrete; it has been deemed necessary to vibrate the mold box in which the article is formed, rather. violently or at relatively high speeds in order to obtain the desired degree of compactness in. the finished product. Usually, thevibratory motion has consisted in reciprocating the mold box at a high rate of speed under which circumstances the traveler throw of the reciprocating box had to be very limited, not exceeding one-sixteenth of an inch. This limited movement was necessitated by reason of the weight of the mass of concrete or other material used in making the block or other unit because the inertia of this mass, if movedany appreciable distance at the prevailing high rate of speed, would be such that excessive strains or stresses would be set up each time the direction of movement of the mass was reversed. This is quite evident from the fact that practically all concrete molding apparatus of the prior art having reciprocating mold boxes were provided with stops for limiting the amplitude of movement of the mold box in an effort to minimize the load imposed on the vibrating mechanism in reversing the direction of movement of the box. However, the presence of such steps resulted in transmitting terrific stresses to other structural parts of the apparatus, particularly when the mold box was reciprocated at high speeds. This, of course, was quite disadvantageous in that such stresses unduly fatigued the materials of which the machine parts were made. I have discovered that it is not necessary to reciprocate or vibrate the mold box of machines for molding concrete and equivalent heavy materials at such high'rates of speed and, further, that by reducing the speed of operation not only is the life of the apparatus prolonged but, in addition, the amplitude of movement of the mold box can be increased-so that the faces of the block which are disposed parallel to: the path of movement of the mold box during the molding operation can be given a troweled effect so as to possess a smoother finish when removed from the mold. That is, by reducing the speed at which the'box is reciprocated and lengthening'the throw or extent of movement of the box, a troweling eifect is'produced on thoseparticular faces ofthe block as thelmass of concrete has an opportunity to moverel'atively to the inner wallsior liners of the i'mial'dlzioxand also relatively to cores that may beused, each time the direction of movement of the mold box is reversed.

The primary object of the present invention, therefore, is to provide a method for molding con- V 2 crete blocks and the like vina mold box which i reciprocated by harmonic motion at a comparatively low speed and for a .relatively'long distance whereby the strains and stresses set up in the apt-- paratus are minimized and the blocks are molded with smooth or troweled side and core faces.

With these and other objects in View, the in,- vention consists in certain details of construction and combinations and arrangements of parts, all as will hereinafter be more fully described and the novel features thereof particularly pointed out in the appended claim.

In the accompanying drawing- Figure 1 is a front elevational view, partly in section, illustrating the presently preferred form of apparatus for practicing the invention;

Fig. 2 is an end elevation, partly in section;

Fig. 3 is atop plan view; and

Fig. 4 illustratesmore'or less diagrammatically a modified form of apparatus.

In the form of apparatus illustrated in Figs. 1 to 3, the mold member or box l E! is adapted to be reciprocated in guideways l I mounted on side frame members 12. These guideways' H- are attached to upright channel members l3 supported on theside frame members 12 and to lend rigidity to the channel members and ways, cross members M are mounted on the upper ends of the channels and connected to the side frame members by braces IS.

The mold box, or other molding member, is carried on what is termed the mold supporting table It although the latter is essentially a guide member for the mold box in that the ends of this so-called table engage in the ways I l to guide the box in its reciprocatory motion. The ends of the table It may be formed with guide pieces H which engage in the ways I I and preferably, but not necessarily, have an extended bearing onsaid ways. Preferably, also, the-,reciprocatory motion of the mold box isderived from a crank shaft I! whose cranks are directly connected to the mold box support or table by connecting rods I 8, which are pivotally attached to the mold box support or table. The mold box; which may be open at the top thereof, and the. pallet l9; are securely and rigidly mounted on the. table iiibu .as-thfi manner of attachment forms no part-of the pres ent' invention and willvary with the construction of the mold, no particular means of attachment are disclosed. As will be apparent, rotation of crank shaft I'I raises and lowersthe connecting rods l8 toimpart a reciprocatory motion to the As previously stated, the present invention contemplates reciprocating the loaded box by harmonic motion, comparatively slowly and for a relatively greater distance, as compared with prior practices. For this reason, the shaft 1 I is driven to rotate at a speed of between 500 R. P. M. and 2000 R. P. M. and the cranks of said shaft have a throw or off-set of a minimum of one-sixteenth of an inch so that the mold box, together with :the'table', travels a distance of a minimum of one- -eighth of an inch between its limits of movement. For the best results, it is believed, at present, that the total movement of the mold box should not exceed one inch. Also, as previously pointed out, this decreased speed permits increased distance of travel for the reciprocating box, minimizes fatigue strains set up in the apparatus and produces a troweled effect or finish on the side and core faces of the molded unitthat is, the unit surfaces which are parallel to the line of movement of the box during the molding of said unit. In actual practice, excellent results both as to the compaction of the material and the troweling efiect, have been obtained with the crank shaft upper and lower segments of the circular path in which they travel, the vertical movement of the table andbox will be decelerated as compared with the speed at which they move between those two segments of the path of travel of the cranks. Thus, each time the mold box approaches its upper and lower limits of travel, its rate of movement will be decreased, this reduction in its rate of movement taking plac immediately preceding each of the two points at which the direc-' tion of movement of the box is reversed. This feature is especially advantageous in connection with both the method and apparatus of the present invention. So far as concerns the apparatus, it is unnecessary to provide any means, other than the actuating connections between the table and crank shaft, for limiting the amplitude of stresses on any portion of the machine. As to the method, the deceleration of the rate of movement of the box immediately before the direction of movement thereof is reversed affords time or opportunity for the mass Within the box to move under the influence of' its inertia relatively to the side walls and cores of the box, thus producing the troweled effect on the corresponding surfaces of the molded unit as previously described.

'For these reasons, the use of the crank shaft and connecting rods is believed to represent the preferred means for reciprocating and vibrating the mold box, although it will be appreciated that the present method can be practiced with other .directly to the mold box structure.

4 types of vibrating apparatus including the offbalanced shaft vibrating mechanism commonly used in the art by properly regulating the speed and extent of reciprocatory movement imparted to the mold box to comply with the requirements regarding these factors as disclosed herein.

In the modification illustrated in Fig. 4, the use of a separate table or mold supporting member may be eliminated by constructing the box with extensions 20 which engage in the guideways ll.- Where this arrangement of the mold box is used,-

the plate I9 is held firmly against the bottom of the mold by suitable securing means such, for instance, as shown in said Patent No. 2,342,440, and the connecting rods iii are pivotally attached In this case, or in other similar arrangements of the mold box and pallet, the molded block, resting on the pallet is ejected downwardly and out of the mold box by an ejector head (not shown)--and the mold box remains in place.

Where a crank shaft is used for imparting reciprocatory motion to the mold box there is a tendency on the part of the box to move laterally as the cranks approach and leave what might be described as their horizontal positions. In the treatment of heavy loads, as in molding concrete blocks, this tendency of the box to move laterally can be compensated for by the use of the comparatively long guides H engaging with a close fit in the elongated guideways H, in conjunction with the rigidity with which said guideways are supported on the machine frame. However, the use of extended guides is not absolutely essential although it is believed the troweling action previousy described is augmented or more efliciently performed if the travel of the mold box is confined to a substantially straight line movement.

What is claimed is:

T e method. of molding building blocks and similar units of heavy plastic material such as concrete with certain surfaces of the blocks possessing a troweled effect, the steps of loading a mo d box with a volume of said plastic material less than the volumetric capacity of the box, reciprocating the loaded box with a harmonic motion in a linear path parallel to the certain surfaces to be troweled a distance not less than oneeighth of an inch and at a rate not exceeding 2000 cycles per minute, the contents'of the box being free to move relatively to the walls thereof in the direction of reciprocation whereby a troweled effect is produced by said walls on said certain surfaces of the molded unit, the inter mittent reduction in the speed of reciprocation of the box serving to increase the troweled effect of said surfaces of the molded unit.

CHARLES W. AKERS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS- Schutt 'Apr. 2, 1945 

